These Nazi baddies will be led by evil doppelgangers of several Arrowverse heroes, including a villainous Kara Zor-El whom Supergirl star Melissa Benoist has described as “not so nice.” Arrow lead Stephen Amell – who plays Oliver Queen, a.k.a. The Green Arrow – has also been hyping up the crossover event, promising fans that it will feel like a “four-hour movie.”

Routh, who debuted as Ray Palmer/The Atom on Arrow before moving over to Legends, has been talking about one particularly interesting scene from the crossover. The assembled heroes of The CW will unite on the Legends’ trusty Waverider, which Routh has described to CBR as “insane”:

“Yeah, we used to get upset about have 9 people, or 9 characters on the bridge and figuring out how to shoot that, but having 21 or whatever it was is pretty insane. But Greg Smith, who was our director for our episode, knew what he wanted pretty quick. You have to have your ducks in a row when doing a crossover because people are coming from four different shows, like ‘We have Melissa for 2 hours and we have Grant for an hour, and we have Stephen for 30 seconds’ so gotta get the shot!”

It certainly sounds like a crowded scene, with 21 characters vowing for attention within the confines of the Legends’ Timeship. As ever, it should be fun to see The CW’s superheroes sharing screen time and acting out plenty of quips. The Waverider is often a very funny place, but with Barry, Kara and everyone else added to the mix, it seems safe to expect even more laughs than usual during the crossover, thanks to all the heroic and inter-show banter.

However, there is also a serious side to this crossover event. Legends of Tomorrow executive producer Phil Klemmer has already teased that, although there are “some ludicrous moments” in the crossover, there is also “this thing that happens that will honestly move you to tears.” To find out how all those heroes can fit in one scene, how the tonal balance will work, and what this tear-jerking element will be, you’ll just have to tune in next week.